1. Field of the Invention
The present invention relates to a welding gun that is used in spot welding or the like. More specifically, the present invention relates to a welding gun that can prevent penetration of foreign matter into a hollow motor rotating mechanism provided with a hollow rotor rotatably accommodated inside a housing.
2. Related Art
Conventionally, a welding gun for spot welding has been used when overlapping and welding plate materials. In the welding gun, among a pair of electrode tips disposed to sandwich welding target members, one electrode tip is fixed and the other electrode tip is made to approach the welding target members and spot welding is performed. Thereafter, the other electrode tip is made to separate from the welding target member in order allow the welding target members to be moved.
As such a welding gun, a C-type welding gun has been known that is attached to a leading end of a robot arm, for example, and welds works that are retained between electrodes by linearly moving a moveable electrode tip relative to a fixed electrode tip (for example, refer to Japanese Unexamined Patent Application Publication No. 2002-346756). With this welding gun, a pressing rod is made to reciprocally travel by way of applying torque to a feed screw mechanism under the rotational action of a hollow motor rotating mechanism, whereby the moveable electrode tip connected to a leading end portion of the rod is made to approach or separate with respect to the fixed electrode tip. By configuring in this way, it is possible to weld works by causing electric current to pass between the electrode tips provided to a leading end of the welding gun, while compressing and retaining the works.
In addition, the above-mentioned welding gun includes an encoder that detects the rotation angle of a rotor applying torque on the feed screw mechanism in the hollow motor rotating mechanism. The welding gun plots the position of the moveable electrode tip from the rotation angle of the rotor detected by the encoder and the pitch of the feed screw mechanism, and causes the moveable electrode tip to approach or separate with respect to the fixed electrode tip.
Such a welding gun is made in a configuration with only a support bearing between the hollow rotor, which is made to rotate integrally with the threaded shaft of a ball screw that causes the pressing rod to reciprocally travel, and the housing that mounts the stator of the hollow motor rotating mechanism. As a result, foreign matter such as water and welding sputter may penetrate into the hollow motor rotating mechanism, which is enclosed by the housing and the hollow rotor. In this situation, in order to protect against the penetration of foreign matter into the hollow motor rotating mechanism in the welding gun of Japanese Unexamined Patent Application Publication No. 2002-346756, an oil seal is provided at an outer side of the support bearing supporting the pressing rod to protect against the penetration of foreign matter.
In addition, heat is generated in welding guns as a result of causing high current to pass between the electrode tips when performing spot welding. The heat generated from the welding gun is cooled by providing water passages in the welding gun for cooling, and flowing coolant in these water passages. However, if the coolant leaks from these water passages and this coolant reaches the encoder through the inside of the hollow motor rotating mechanism, a short circuit or the like will occur in the electronic substrate, a result of which a detection malfunction may occur in the encoder, and the position of the moveable electrode tip may not be accurately plotted.
A welding gun in which a seal member is installed is illustrated in Japanese Unexamined Patent Application Publication No. 2002-346753. This welding gun causes one electrode tip attached to a leading end portion of a rod of a feed screw mechanism, which is coupled to a hollow motor rotating mechanism, to open and close relative to another electrode tip that is fixed, by causing the rod to reciprocally travel. In addition, a seal member is installed in this welding gun at a holder leading end of a bushing that supports the reciprocally travelling rod. For this welding gun, it has been considered that there is room for improvement in the waterproofing property against coolant penetrating from between the motor housing and the hollow rotor to inside the motor housing when exchanging electrode tips.